Look at the drawing in the 2nd post by Dale Meisenheimer in this webpage;
http://www.artglassanswers.com/forum...php?f=22&t=150 .
Move the slider on the right of the drawing so all of the dark blue wording and lines are visible.
He shows how the "make up air" comes in through the wall and is ducted up to the back of the torch bench.
This air flow can be a major portion of the air (up to 85%) going up through the flame / fume zone and outside through the ventilation fan with the other 15% coming from behind you around your body and over your shoulders, giving you fresh air to breath, and then outside through the ventilation fan.
I am still looking for actual pictures of studios with make up air ducted like this. I know I have seen some here in the LE studio threads, I just haven't found them yet.
They look just like the floor registers used to bring heat from a forced air furnace to rooms in a home.
I will keep looking for them for you.